Saturday, October 22, 2016

Images of Ioat different near-infrared wavelengths show bright spots that are thermal emissions from the moon’s myriad volcanoes. Click on image to see the entire set, with the name of the near-infrared filter indicated in the black box at the start of each section. Note the increasing number of hot spots detected at longer wavelengths, i.e. towards the bottom of the figure. (Katherine de Kleer and Imke de Pater image, from Gemini Observatory/AURA & Keck Observatory).

All hot spots detected are shown on amap of Io. Each circle represents a
new detection; the size of the circle corresponds logarithmically to
the intensity, and more opaque regions are where a hot spot was detected
multiple times. The color and symbol indicate the type of eruption,
following the legend. Loki Patera is at 310 West, 10 North and
Kurdalagon Patera is at 220 West, 50 South.

Video showing all hot spots detected from August 2013 through
December 2015, displayed on a full map of Io and illustrating the
approximate length of time they were visible. The size of the circle
corresponds logarithmically to the intensity. Loki Patera is at 310 West
longitude, 10 North latitude and Kurdalagon Patera is at 220 West
longitude, 50 South latitude. (Credit: Katherine de Kleer and Imke de
Pater, UC Berkeley).Youtube

High-resolution image of Io, showing hot spots — Loki Patera and
Amaterasu Patera — visible from Earth only with adaptive optics on the
planet’s largest telescopes, Keck and Gemini.

Press release issued by the University of Berkeley to
coincide with presentation at the joint 48th annual meeting of the
Division for Planetary Sciences (DPS) of the American Astronomical
Society (AAS) and 11th annual European Planetary Science Congress
(EPSC).

Jupiter’s moon Io continues to be the most volcanically active body
in the solar system, as documented by the longest series of frequent,
high-resolution observations of the moon’s thermal emission ever
obtained.

Using near-infrared adaptive optics on two of the world’s largest
telescopes — the 10-meter Keck II and the 8-meter Gemini North, both
located near the summit of the dormant volcano Mauna Kea in Hawaii —
University of California, Berkeley, astronomers tracked 48 volcanic
hotspots on the surface over a period of 29 months from 2013 through the
end of 2015.

Without adaptive optics — a technique that removes the atmospheric
blur to sharpen the image — Io is merely a fuzzy ball. Adaptive optics
can separate features just a few hundred kilometers apart on Io’s
3,600-kilometer diameter surface.

“On a given night, we may see half a dozen or more different hot
spots,” said Katherine de Kleer, a UC Berkeley graduate student who led
the observations. “Of Io’s hundreds of active volcanoes, we have been
able to track the 50 that were the most powerful over the past few
years.”

She and Imke de Pater, a UC Berkeley professor of astronomy and of
Earth and planetary science, observed the heat coming off of active
eruptions as well as cooling lava flows and were able to determine the
temperature and total power output of individual volcanic eruptions, as
well as track their evolution over days, weeks and sometimes even years.

Interestingly, some of the eruptions appeared to progress across the
surface over time, as if one triggered another 500 kilometers away.

“While it stretches the imagination to devise a mechanism that could
operate over distances of 500 kilometers, Io’s volcanism is far more
extreme than anything we have on Earth and continues to amaze and baffle
us,” de Kleer said.

De Kleer and de Pater will discuss their observations at a media
briefing on Oct. 20 during the joint 48th meeting of the American
Astronomical Society’s Division for Planetary Sciences and 11th European
Planetary Science Congress in Pasadena, California. Papers describing
the observations have been accepted for future publication by the journal Icarus.

Tidal Heating

Io’s intense volcanic activity is powered by tidal heating: heating
from friction generated in Io’s interior as Jupiter’s intense
gravitational pull changes by small amounts along Io’s orbit. Models for
how this heating occurs predict that most of Io’s total volcanic power
should be emitted either near the poles or near the equator, depending
on the model, and that the pattern should be symmetric between the
forward- and backward-facing hemispheres in Io’s orbit (that is, at
longitudes 0-180 vs. 180-360).

That’s not what they saw. Over the observational period, August 2013
through December 2015, the team obtained images of Io on 100 nights.
Though they saw a surprising number of short-lived but intense eruptions
that appeared suddenly and subsided in a matter of days, every single
one took place on the trailing face of Io (between 180 and 360 degrees
longitude) rather than the leading face, and at higher latitudes than
more typical eruptions.

“The distribution of the eruptions is a poor match to the model
predictions,” de Kleer said, “but future observations will tell us
whether this is just because the sample size is too small, or because
the models are too simplified. Or, perhaps we’ll learn that local
geological factors play a much greater role in determining where and
when the volcanoes erupt than the physics of tidal heating do.”

One key target of interest was Io’s most powerful persistent volcano,
Loki Patera, which brightens by more than a factor of 10 every 1-2
years. A patera is an irregular crater, usually volcanic.

Many scientists believe that Loki Patera is a massive lava lake, and
that these bright episodes represent its overturning crust, like that
seen in lava lakes on Earth. In fact, the heat emissions from Loki
Patera appear to travel around the lake during each event, as if from a
wave moving around a lake triggering the destabilization and sinking of
portions of crust. Prior to 2002, this front seemed to travel around the
cool island in the center of the lake in a counter-clockwise direction.

After an apparent cessation of brightening events after 2002, de Pater observed renewed activity in 2009.

“With the renewed activity, the waves traveled clockwise around the lava lake,” she noted.

Another volcano, Kurdalagon Patera, produced unusually hot eruptions
twice in the spring of 2015, coinciding with the brightening of an
extended cloud of neutral material that orbits Jupiter. This provides
circumstantial evidence that eruptions on the surface are the source of
variability in this neutral cloud, though it’s unclear why other
eruptions were not also associated with brightening, de Kleer said.

De Kleer noted that the Keck and Gemini telescopes, both atop the
dormant volcano Mauna Kea, complement one another. Gemini North’s queue
scheduling allowed more frequent observations — often several a week —
while Keck’s instruments are sensitive also to longer wavelengths (5
microns), showing cooler features such as older lava flows that are
invisible in the Gemini observations.

The astronomers are continuing their frequent observations of Io,
providing a long-term database of high spatial resolution images that
not even Galileo, which orbited Jupiter for eight years, was able to
achieve.

The joint 48th meeting of the Division for Planetary Sciences (DPS) and
11th European Planetary Science Congress (EPSC) in Pasadena, California,
is second time DPS and EPSC have been joined into one meeting. The goal
of the joint meeting is to strengthen international scientific
collaboration in all areas of planetary science. This is the first time
that EPSC, which provides the dissemination platform for the Europlanet
2020 Research Infrastructure, is held outside Europe. For more
information, see: https://aas.org/meetings/dps48. Follow: #dpsepsc,
@DPSMeeting, @europlanetmedia, and @AAS_Press on Twitter.